QTTATEENAET FAUNA OF GIBEALTAE. 55 



Prison, this plateau is about 400 feet above the sea; and it slopes gradually to the 

 south at an angle of about 11°, so that at its southern boundary, which is in a 

 vertical inland cliff about 100 feet high, its level above the sea is from 250 to 300 

 feet. It is bounded on the east and west sides by nearly perpendicular cliffs, whose 

 base is in a terrace about 100 feet above the sea-level. 



The southernmost division of the rock (d), termed Europa Flats, is also a tolerably 

 even plain, which gradually slopes to an elevation of not more than 50 feet above the 

 level of the water. The sea-bottom, where visible in calm weather at the base of the 

 eastern cliffs of the Europa Plateau, and beyond the masonry with which its southern 

 flank is covered, also constitutes a rocky plain, with precisely the same waterwom 

 surface as that of the " Windmill Hill " and Europa Plateau, and constituting, in fact, 

 a third level or step. That part of this lower plain which was above water was formerly 

 termed the Lower Europa ; but it is now entirely concealed by the military works. 



The eastern face of the rock is a nearly perpendicular precipice, being, in fact, the 

 escarpment of the limestone strata. Upon this face, where they have not been removed 

 by denudation or weathering, a succession of sea-worn terraces, one above the other, at 

 distances of about 100 to 150 feet, may be observed up to a height of 800 or 900 feet, 

 apparently indicating so many successive stages of elevation. The western face forms 

 an irregular slope, interrupted by longitudinal cliffs and ravines, and gradually shelving 

 at the bottom into a gentle declivity, partly talus, upon which the town is chiefly built. 



With the exception of some ferruginous sands and shales on the western flank, the 

 mass of the Rock of Gibraltar consists of hard grey Jurassic limestone. Wherever 

 the surface is sufficiently exposed the rock is seen to be traversed throughout by innu- 

 merable ramifying fissures, which occasionally widen out into extensive caverns, either 

 partially empty or, as was formerly seen at Rosia Bay, completely filled with ossi- 

 ferous breccia. 



The principal reason of this fractured condition is undoubtedly to be sought in the 

 circumstance that the strata have been subjected to very great disturbances. They 

 have, in fact, been twisted, as it were, in different directions. This is shovm very plainly 

 by the fact that the angle of the dip varies very much in different parts — to such an 

 extent, indeed, that its direction is reversed at the opposite extremities of the pro- 

 montory. These changes, moreover, are very abrupt ; and the points at which they 

 take place seem to correspond with the two lines of fracture termed "Quebradas" 

 (a, b, fig. 1, p. 54), and with the line of passage from the elevated to the lower portion of 

 the rock (c). And it is precisely at or near these lines of fracture that the principal 

 known caves and fissures are situated. 



But, besides the movements by which the strata have been thus affected, Mr. Smith 

 is of opinion, and has pretty conclusively shown, that the whole mass of the rock has 

 been elevated and depressed more than once to the extent of its entire height, even 

 " since the testaceous fauna was the same as at present." 



I 2 



